There are many situations in which an injection needle is required to be shielded after use to prevent the risk of needle stick injury. This applies not only to single use devices such as disposable syringes and the like, but also to multiple use devices such as cartridges, or pen-type injectors, where a disposable needle is secured, e.g. by screwing or other suitable connection action, into a cartridge or adaptor and replaced for each subsequent injection. Such disposable needles for use with injection devices such as autoinjectors are commonly referred to as “pen needles”. The safe shielding of such needles is especially important in clinics and hospitals where the user is injected by a clinician, where the risk of cross-infection is greater.
It is known to provide a removable or detachable shield or protector which is mounted on the forward end of a needle assembly covering the forward tip of the needle. The shield can be removed to carry on the injection and replaced over the needle afterwards. This type of shield can easily get lost or damaged during the injection process. Shields are also known which require the user to grip the medical instrument in one hand and twisting or push an actuator with the other. With either of these arrangements, the user is likely to approach it from the front or side, thus increasing the risk of inadvertent needle stick injury. Further, it is desirable that after a single use, that the needle is not used again, since this increases the risk of cross infection and of tissue damage from blunted needles.
Shield arrangements are also known which are biased towards a position in which the needle is covered such that the needle only projects from the shield during the delivery of the injection with the shield automatically moving back into a shielding position as the needle is removed from the skin. However, such arrangements may add significant complexity and cost to a needle assembly (particularly a single use, disposable needle assembly). Further with such devices the user is generally unable to see the needle during insertion which many users may find disadvantageous.
Embodiments of the invention seek to provide improved needle assemblies which may overcome some or all of these problems.